Tape storage devices for writing data to tape are known of the type comprising helical-scan recording means operative to write to tape in a succession of tracks each having a data area for the storage of data; and signal processing means operative to receive first data signals, representative of first data to be stored, and to process said first data signals to generate and output track signals to said recording means whereby to cause the latter to write the first data to tape in accordance with a predetermined format in which said first data is stored in the data areas of one or more groups of tracks with further tracks, hereinafter "amble" tracks, being used to perform auxiliary functions, the said groups of tracks and said amble tracks being such as to permit them to be distinguished from each other upon reading. Such tape storage devices are generally also arranged to read tapes written in accordance with said predetermined format, although a separate tape storage device may be provided for this purpose. Thus, tape storage devices for reading data from tape are known of the type comprising helical-scan reading means operative to read a tape written in accordance with said format and to output track signals representative of the tracks recorded thereon; and signal processing means operative to receive said track signals from the reading means and to process said track signals to generate and output first data signals representative of said first data recorded in the data areas of the groups of tracks, this processing involving distinguishing signals derived from said groups of tracks from signals derived from said amble tracks whereby to avoid any contents of the amble tracks being treated as first data.
Tape storage devices of the aforesaid types include storage devices operative to write/read data to/from tape in accordance with the Digital Data Storage (DDS) format described in the document "Digital Data Storage Format Description" (Revision B, October 1988) available from Hewlett-Packard Limited, Bristol, England. The DDS format is based on the DAT digital audio recording format but includes modifications and extensions to the basic DAT format to render it suitable for storing computer data. For a storage device implementing the DDS format, the aforesaid first data is constituted by the computer data, this data being stored in groups of tracks that are optionally separated by amble tracks.
Because computer data is essentially asynchronous (by which is here meant that it does not need to be provided at a constant transfer rate), the DDS format does not need to include the same amount of first data in every track but can afford to have an uneven distribution of data between tracks. More particularly, as well as the amble tracks not being available for first data, at least a portion of one or more tracks of each said group of tracks is used to store an index of record and file separators relating to the first data held in the group.
For certain applications it would be useful if both computer data and audio data could be at least read by the same DDS storage device.
One possible way of achieving this would be to arrange for the DDS device to be able to play a tape written on a DAT audio player. The underlying format of the DDS drive is the 48 KHz mode of the DAT specification so that much of the DDS storage device electronics is similar to that of a DAT player. However, for this approach to work the DDS storage device would need to be altered to recognize the DAT format and read the audio data, as well as cope with the absence of a lead-in area as is provided on a DDS tape. Furthermore, that part of the DDS device electronics expecting to find data organized into groups would need to be disabled or bypassed. Clearly, this approach would require substantial redesign of a standard DDS-only tape storage device.
A different approach would be to store audio data as first data within groups of tracks in accordance with the DDS format. However, as already mentioned, the storage of data in groups is really only suitable for asynchronous data rather than synchronous data, such as audio data, where a steady transfer rate is needed. In order to overcome the transfer rate fluctuations that would be caused by amble tracks and group indexes a substantial data buffer would be required with the attendant cost and complexity. In addition, some way would need to be found to distinguish audio data from computer data so that the former is not mistaken for the latter.